• 3.9 baseline — 0.6 × season 3.8 (11 gm) + 0.4 × last 10 4.0
• −0.5 opponent leak — they concede 80.8/game vs a 93.4 league average
• +1.0 at this ground — averages 4.9 there (50 gm)
• vs them: averages 6.2 over 5 games — evidence, never summed

Derived, not measured — plain arithmetic over his real games, shown in full. Adjustments can overlap (a game at this ground can also be a wet one); they add simply, and this note is the admission. Round 6: 8 — far outside his usual range; kept in the average, not smoothed away.